The radio ad begins with a sentence of apparently scrawled language, the kind Microsoft boldly claims Google’s Gmail users have to take up if they want to prevent the search major from checking their messages to garner personal data and make money by selling it to marketers.

The voice-over ad then states: "Pig Latin may be hard to understand, but you probably need it if you use Gmail, because Gmail scans every word of your emails to sell ads.

"But Outlook.com doesn’t. And you can choose to opt out of personalised ads," it continues.

"To stop Gmail from using your e-mails, use Outlook.com. Learn more at KeepYourEmailPrivate.com and keep your emails ivatepray".

Microsoft claimed Outlook.com boasted improved privacy options compared to Gmail, and that Outlook.com only carried out protective scanning of emails for bugs and spam, which was also supported by the watchdog.

ASA said in a statement that Microsoft believed that the two types of scanning were different, as targeting required the collation and retention of data whereas protective scanning did not, and considered that the use of personal data was likely to be a privacy concern for some consumers.

"Because the ad made clear that the privacy claims were in relation to ad targeting, which Outlook.com does not carry out, we therefore concluded that the ad was not misleading," the watchdog added.

However, in another case, Microsoft had allegedly went through a French blogger’s Hotmail email account in search of the source of a leaked Windows 8 code.